We are interested in investigating the molecular properties of cell membranes with a view towards understanding the critical events that occur at the lymphocyte plasma membrane during activation by antigens and mitogens, and other membrane-related immunological phenomena. The possible involvement of actomyosin-like protein systems associated with the membranes of lymphocytes will be studied with antibodies to myosins prepared from smooth and striated muscles, to look for possible immunologically related components. The induction of the biosynthesis and membrane localization of IgM after antigenic modulation of B lymphocytes with anti-IgM antibodies will be studied by electron microscopy, using immunoferritin techniques for the intracellular localization of newly synthesized IgM.